Help!!

I'm at my wits end now. My little boy is nearly 3 and has been potty training for a few months. First few weeks he had accidents as to be expected then it clicked and he would tell me when he needed to poo or wee. We hadn't had any accidents for weeks and now for the last week or so he is having accidents every day and he doesn't tell me when he needs to go. When I get cross he just laughs like he doesn't care. Today he wet himself and didn't even come and tell me. Why has he gone so backwards!? I thought I'd cracked it and now I'm so stressed 😫 Help please!